I want to learn how the neural pathways responsible for the production of coordinated motor behavior in adult mammals are formulated during ontogeny and to determine what role the environment plays in augmenting the construction and maintenance of these motor circuits. Therefore, I propose to analyze the ontogenesis of brain stem circuits that govern eye posture and movement. Specifically, the aims of this research proposal are two-fold: 1) to correlate the morphogenesis of the ocular motoneurons and their synaptic inputs with the onset and maturation of reflex eye movements in neonatal kittens and rabbits, and 2) having established the normal developmental sequence, to assess the potential for modification of these programs as a result of differential sensory experience during maturation. The first goal will be achieved by combining behavioral and morphological observations in the same animal. After determining the characteristics of developing eye movements in response to appropriate vestibular and optokinetic stimuli, the animal will be prepared for light and electron microscopic analyses of the eye motor nuclei. Furthermore, experimental lesions will help to ascertain the structure and deployment of the excitatory and inhibitory projections eminating from the vestibular nuclei. During phase 2, postnatal animals will be reared in experimentally modified visual or vestibular environments and then tested with a similar morphological and behavioral protocol.